Rf/Humming

9m2ody · Post by **9m2ody** » Thu Jan 20, 2011 7:56 pm

Hi there,

Recently, play around with audio..really love to hear all hams with very nice audio on the air..so, right now i was facing problem with my antenna & audio chain..this happen when i turn my beam to NW & SW, the RF/hum will coming to my radio once i push PTT..but if i turn to others side..it's was ok..what i found are the RF/hum come from mic..i tested with push PTT then unplug the mic cable & the humming no more..what suppose i do? hope Guru can help me..

i'm using studio condenser mic (AT2035)

Thanks

Ody

Post by **Voodoo Guru** » Fri Jan 21, 2011 9:39 am

Howdy Ody,
Welcome to the Forum!
Great to have you here.

That sounds like you are getting a classic case of Mr. Ruffy (RFI) introduced into the microphone or microphone cable. The reason it seems to change with the antenna in different directions is because the high power lobes of the RF envelope will saturate the mic or mic cable.

There can be many different solutions to this problem.

1 - add Mix #31 Ferrite cores to the Microphone cable at each end, and in the middle.

2 - Be sure the mic cable is wired in a Balanced configuration.

3 - Change the microphone cable to a good quality cable like Canare or Mogami Starquad. Whatever brand name it is, be sure to get the Starquad.

4 - Shorten the mic cable to the minimum length necessary to make it to the preamp, you do not want an excess all coiled up somewhere as this length may wind up being at a resonant frequency of the transmitted RF.

5 - You might try lifting the ground pin on the AC Line plug going to the Preamp which is supplying the Phantom Power to the Mic. Sometimes this helps.

6 - Add a .001uf cap from the #2 Pin to #1 Pin, and a .001uf cap from the #3 pin to the #1 in the XLR connectors of the mic cable for RFI bypass.

6 - If all else fails, change the mic and see if that cures the problem, your antenna may just be too close to the shack for that microphone to operate correctly in an RF Field.

Hopefully one of these solutions will help you on your problem.
Good Luck, RFI can be very frustrating.
Take Care,

9m2ody · Post by **9m2ody** » Sat Jan 22, 2011 12:41 am

Hi Voodoo Guru,

Nice to know you here..

Thanks a lots for the info..i will try according the kind of advise..for time being i just put 'Cylindrical Magnet' at the end of mic cable, it was help but still can hear a little bit Mr Ruffy..hi hi hi..

will let you know after my 'Ruffy' gone soon..

Thanks,

9m2ody · Post by **9m2ody** » Sun Jan 23, 2011 1:13 am

Hi Voodoo Guru,

Right now i'm done on my audio problem with put a few magnet toroid snap at microphone cable at each end and in the middle..& still facing problem at 15m band while beam turn to SW..but i solve it by reduce master volume at mixer..after all, it's was ok & no more RFI coming..my question is, it is the correct way to reduce RFI?

Thanks,

Ody

Post by **Voodoo Guru** » Sun Jan 23, 2011 4:48 pm

Howdy Ody,

Well the main thing is to not have the RFI.
if those measures remove it from your audio then we would say yes!

Have Fun!

!KANT · Post by **!KANT** » Thu Jan 27, 2011 2:17 pm

Guru has provided excellent information [as expected]. Only addition I can provide/suggest is to invest in a Line Isolator for further reducing or complete elimination of RFI (if you haven't already installed one). They're a great investment and do the intended job of RFI suppression.

Good luck and keep us updated.

9m2ody · Post by **9m2ody** » Thu Jan 27, 2011 9:57 pm

Hi !KANT,

After all out, i have no more facing with RFI problem right now..about line isolator, i have done a homebrew iBox & very happy with my set up right now even the 'weakest link' are ic718 & ts570d (only 2.4k bandwidth)..but really enjoy..may be in future i will buy another rig which is can support up to 3k & more bandwidth..

Thanks,

ody